1. Field of the Invention
This invention relates to sensing oxides of nitrogen in an environment such as, for example, the exhaust flow from an internal combustion engine.
2. Prior Art
Various semiconductor gas sensors based on SnO.sub.2 have been develoepd which exhibit sensitivity to oxides or nitrogen but, at the same time, also respond to a variety of other molecules such as carbon monoxide, hydrogen, hydrocarbons, etc. This lack of selectivity is particularly disadvantageous if such semiconductor gas sensor is used in connection with internal combustion engine control applications. That is, it is difficult to sense oxides of nitrogen in the exhaust from the engine because carbon monoxide, hydrogen, hydrocarbons and other reducing species are always present in the exhaust gas usually in greater concentrations than the oxides of nitrogen.
As a result, such known simple and inexpensive oxides of nitrogen sensors have limited use in control applications for internal combustion engines because of their inability to detect oxides of nitrogen in the presence of other gases. Such detection is desirable because the information can be used to provide information to aid and control the operation of the internal combustion engine. These are some of the problems this invention overcomes.